"We have photographs, my Lord!" said Friar Pennsetucky. "We have -"
"Vampires do not show up on cameras, you halfwit," said Mrs. Hwost, slapping the empty photographs from the Friar's hand. 
"A sign of the devil?" said the Friar as though this was new to her.
"Lacking souls, they cannot be reflected in the physical," said Hwost. "Paintings of them fade, sculptures crumble - you cannot copy what is not truly there."
"God's Wounds!" said the Friar.
"By a likewise principle there will be little astrological evidence," said Hwost. "We primarily locate the forces of the Archenemy when they interfere with the destinies of mortals. When they simply cower they are difficult to track."
"We must drive the beast into the open!" said the Friar.
"On this, the good Friar is correct," said Hwost. "If they can be made to interfere in the destinies of mortals then they shall become increasingly visible to the Sight - and plans can be laid around them."